Field of the Invention
The invention relates to a device for electrically heating a fluid, particularly for use in an electrically operated motor vehicle, the device has an induction coil, which is integrated in an oscillating circuit and generates an alternating magnetic field, and at least one first inductor, which is positioned within the alternating magnetic field.
Description of the Background Art
Today, vehicles operated with internal combustion engines are mostly heated by heating a fluid, which is usually a water/glycol mixture. The fluid that is intended first and foremost for cooling the internal combustion engine is passed through a water to air heat exchanger after it has taken up the heat of the internal combustion engine. The air, which as a cooling fluid flows around the water to air heat exchanger, hereby takes up the thermal energy from the cooling fluid. The cooling fluid is cooled in this way and the air is heated. The heated air is then conveyed into the interior of the vehicle and thereby used for controlling the temperature in the interior.
In vehicles without an internal combustion engine or in high-efficiency diesel engines, there is no waste heat from the engine or it is not sufficient to adequately heat the vehicle cabin according to the driver's wishes. To circumvent this, electrical heaters are being used currently to convert electrical energy into heat. There are essentially two alternatives here. In the first alternative, the air flowing in the interior is heated directly by an electrical auxiliary heater. Such implementations are known, for instance, from EP 1 935 684 A1.
For this purpose, the auxiliary heater is positioned in a region of the interior air intake such that before the air is conveyed into the interior it comes into contact with the electrical auxiliary heater and thus takes up heat. The auxiliary heaters are often installed directly in the vicinity of or on the heat exchanger itself that is provided for heating the air stream by means of the heated cooling water from the combustion engine. This creates an additional parts cost and, moreover, the typically used PTC ceramic elements are rather heavy.
As a second alternative, electrical water heaters are prior in the art that first heat a fluid such as, for instance, the water/glycol mixture used for cooling the internal combustion engine. The heated fluid is then conveyed through an additional water to air heat exchanger, as a result of which the air flowing around the heat exchanger is heated.
The principle functions similar to the heating of air, as it occurs, for instance, in combustion engine-operated vehicles, with the difference that the water/glycol mixture is heated electrically and not by the waste heat from the combustion engine.
A particular disadvantage in conventional methods is the required water circuit for the water/glycol mixture and the additional components, such as, for instance, a water pump, pipes, and valves.
However, a water circuit also provides a relatively simple manner to utilize different waste heat sources, such as an electric motor, battery, or power electronic units that in electric vehicles must be actively cooled, which again suggests the use of cooling water circuits.
Especially in light of the discussion of ranges in the case of only a limited battery capacity, water heating is a frequently used technique in electric vehicles. Also, a water heater can be installed in the engine compartment without a high-voltage component needing to be installed in the passenger compartment, which for some vehicle manufacturers represents a safety problem.
Electrical water heaters are currently realized in that one or more heating elements project into the fluid and give off their heat to the fluid. These elements can be simple metal heating coils or also so-called PTC stones/ceramics. The fact that PTC ceramics (PTC=positive temperature coefficient) have a certain intrinsic safety with respect to overheating because of the temperature dependence of their resistance is advantageous with their use.
A basic disadvantage when using such a water heater is that the employed heating elements must be electrically isolated from the fluid they are to heat. This requirement makes the use of such technology expensive and also has a negative effect on the efficiency and response speed of the heating elements.